js图片全屏预览

<img id="thumbnail" src="thumbnail.jpg" alt="Thumbnail" style="width:100px; cursor:pointer;">
<div id="modal" class="modal">
  <span class="close">&times;</span>
  <img class="modal-content" id="full-image">
</div>

.modal {
  display: none; 
  position: fixed; 
  z-index: 1; 
  left: 0;
  top: 0;
  width: 100%; 
  height: 100%;
  overflow: auto; 
  background-color: rgba(0,0,0,0.9); 
}

.modal-content {
  margin: auto;
  display: block;
  width: 80%;
  max-width: 700px;
}

.close {
  position: absolute;
  top: 15px;
  right: 35px;
  color: #fff;
  font-size: 40px;
  font-weight: bold;
  cursor: pointer;
}

var modal = document.getElementById("modal");
var img = document.getElementById("thumbnail");
var modalImg = document.getElementById("full-image");
var span = document.getElementsByClassName("close")[0];

img.onclick = function(){
  modal.style.display = "block";
  modalImg.src = this.src.replace("thumbnail", "fullsize"); // 假设全尺寸图片URL是通过替换"thumbnail"为"fullsize"得到的
}

span.onclick = function() { 
  modal.style.display = "none";
}

window.onclick = function(event) {
  if (event.target == modal) {
    modal.style.display = "none";
  }
}